The merger debris of dwarf galaxies in the local stellar halo

2018 ◽  
Vol 14 (S344) ◽  
pp. 38-41
Author(s):  
Cuihua Du ◽  
Hefan Li ◽  
Heidi Jo Newberg
Keyword(s):  
Angular Momentum ◽  
Dwarf Galaxies ◽  
Solar Neighborhood ◽  
Chemical Information ◽  
Halo Stars ◽  
Data Release ◽  
The Galaxy ◽  
Stellar Halo ◽  
History Of

AbstractBased on the second Gaia data release and spectroscopy from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Data, we identified 23,582 halo stars kinematically. The halo streams in the solar neighborhood could be detected in the space of energy and angular momentum. We reshuffle the velocities of these stars to determine the significance of the substructure. Finally, we find 14 statistically significant substructures and several substructures are not reported by previous works. These structures may be the debris of dwarf galaxies accretion event and their dynamical and chemical information can help to understand the history of the Galaxy.

scholarly journals Stellar orbital properties as diagnostics of the origin of the stellar halo

2015 ◽  
Vol 11 (S317) ◽  
pp. 358-359
Author(s):  
Monica Valluri ◽  
Sarah R. Loebman ◽  
Jeremy Bailin ◽  
Adam Clarke ◽  
Victor P. Debattista ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Milky Way ◽  
Large Fraction ◽  
Disk Galaxy ◽  
Short Axis ◽  
Halo Stars ◽  
The Galaxy ◽  
Stellar Halo

AbstractWe examine metallicities, ages and orbital properties of halo stars in a Milky-Way like disk galaxy formed in the cosmological hydrodynamical MaGICC simulations. Halo stars were either accreted from satellites or they formed in situ in the disk or bulge of the galaxy and were then kicked up into the halo (“in situ/kicked-up” stars). Regardless of where they formed both types show surprisingly similar orbital properties: the majority of both types are on short-axis tubes with the same sense of rotation as the disk – implying that a large fraction of satellites are accreted onto the halo with the same sense of angular momentum as the disk.

scholarly journals Relation Between Star Formation and Angular Momentum in Spiral Galaxies

1983 ◽  
Vol 100 ◽  
pp. 135-136
Author(s):  
L. Carrasco ◽  
A. Serrano
Keyword(s):  
Angular Momentum ◽  
Star Formation ◽  
Radial Distribution ◽  
Spiral Galaxies ◽  
Formation Rate ◽  
Inverse Function ◽  
Solar Neighborhood ◽  
Spin Angular Momentum ◽  
Stellar Formation ◽  
The Galaxy

We derive the radial distribution of the specific angular momentum j=J/M, for the gas in M31, M51 and the galaxy, objects for which well observed unsmoothed rotation curves are available in the literature. We find the specific angular momentum to be anti-correlated with the present stellar formation rate, i.e. minima of spin angular momentum correspond to the loci of spiral arms. We find that the stellar formation rate is an inverse function of j. We derive new values of Oort's A constant for the arm and interarm regions in the solar neighborhood.

scholarly journals The gravitational force field of the Galaxy measured from the kinematics of RR Lyrae in Gaia

2019 ◽  
Vol 485 (3) ◽  
pp. 3296-3316 ◽  
Author(s):  
Christopher Wegg ◽  
Ortwin Gerhard ◽  
Marie Bieth
Keyword(s):  
Dark Matter ◽  
Dark Matter Halo ◽  
Galactic Centre ◽  
Gravitational Acceleration ◽  
Momentum Exchange ◽  
Acceleration Field ◽  
Rr Lyrae ◽  
Halo Stars ◽  
The Galaxy ◽  
Stellar Halo

Abstract From a sample of 15651 RR Lyrae with accurate proper motions in Gaia DR2, we measure the azimuthally averaged kinematics of the inner stellar halo between 1.5  and 20  kpc from the Galactic centre. We find that their kinematics are strongly radially anisotropic, and their velocity ellipsoid nearly spherically aligned over this volume. Only in the inner regions ${\lesssim } 5\, {\rm kpc}\,$ does the anisotropy significantly fall (but still with β > 0.25) and the velocity ellipsoid tilt towards cylindrical alignment. In the inner regions, our sample of halo stars rotates at up to $50\, {\rm km}\, {\rm s}^{-1}\,$, which may reflect the early history of the Milky Way, although there is also a significant angular momentum exchange with the Galactic bar at these radii. We subsequently apply the Jeans equations to these kinematic measurements in order to non-parametrically infer the azimuthally averaged gravitational acceleration field over this volume, and by removing the contribution from baryonic matter, measure the contribution from dark matter. We find that the gravitational potential of the dark matter is nearly spherical with average flattening $q_\Phi ={1.01 \pm 0.06\, }$ between 5 and 20 kpc, and by fitting parametric ellipsoidal density profiles to the acceleration field, we measure the flattening of the dark matter halo over these radii to be $q_\rho ={1.00 \pm 0.09\, }\!.$

The Nature of the Triangulum-Andromeda Stellar Structures

2018 ◽  
Vol 14 (S344) ◽  
pp. 122-124
Author(s):  
J. V. Sales Silva ◽  
H. Perottoni ◽  
K. Cunha ◽  
H. J. Rocha-Pinto ◽  
D. Souto ◽  
...  
Keyword(s):  
High Resolution ◽  
Kinematic Analysis ◽  
Dwarf Galaxies ◽  
Galactic Disk ◽  
Thin Disk ◽  
Atmospheric Parameters ◽  
Chemical Abundances ◽  
The Galaxy ◽  
Stellar Halo ◽  
Debris Cloud

AbstractThe outer stellar halo is home to a number of substructures that are remnants of former interactions of the Galaxy with its dwarf satellites. Triangulum-Andromeda (TriAnd) is one of these halo substructures, found as a debris cloud by Rocha-Pinto et al., (2004) using 2MASS M giants. Would be these structures related to dwarf galaxies or to the galactic disk? To uncover the nature of these stars we performed a high-resolution spectroscopic study (R = 40,000) along with a kinematic analysis using Gaia data. We determined the atmospheric parameters and chemical abundances of Ca and Mg for the 13 TriAnd candidate stars along with their respective orbits. Our results indicate that the TriAnd stars analyzed have a galactic nature but that these stars are not from the local thin disk.

scholarly journals Leaves on trees: identifying halo stars with extreme gradient boosted trees

2018 ◽  
Vol 621 ◽  
pp. A13 ◽  
Author(s):  
Jovan Veljanoski ◽  
Amina Helmi ◽  
Maarten Breddels ◽  
Lorenzo Posti
Keyword(s):  
Phase Space ◽  
New Era ◽  
Massive Galaxies ◽  
Full Phase Space ◽  
Halo Stars ◽  
Machine Learning Model ◽  
Data Release ◽  
Stellar Halo ◽  
Red Giant ◽  
Galactic Astronomy

Context. Extended stellar haloes are a natural by-product of the hierarchical formation of massive galaxies like the Milky Way. If merging is a non-negligible factor in the growth of our Galaxy, evidence of such events should be encoded in its stellar halo. The reliable identification of genuine halo stars is a challenging task, however. Aims. With the advent of the Gaia space telescope, we are ushered into a new era of Galactic astronomy. The first Gaia data release contains the positions, parallaxes, and proper motions for over two million stars, mostly in the solar neighbourhood. The second Gaia data release will enlarge this sample to over 1.5 billion stars, the brightest ~ 5 million of which will have full phase-space information. Our aim for this paper is to develop a machine learning model for reliably identifying halo stars, even when their full phase-space information is not available. Methods. We use the Gradient Boosted Trees algorithm to build a supervised halo star classifier. The classifier is trained on a sample of stars extracted from the Gaia Universe Model Snapshot, which is also convolved with the errors of the public TGAS data, which is a subset of Gaia DR1, as well as with the expected uncertainties for the upcoming Gaia DR2 catalogue. We also trained our classifier on a dataset resulting from the cross-match between the TGAS and RAVE catalogues, where the halo stars are labelled in an entirely model-independent way. We then use this model to identify halo stars in TGAS. Results. When full phase-space information is available and for Gaia DR2-like uncertainties, our classifier is able to recover 90% of the halo stars with at most 30% distance errors, in a completely unseen test set and with negligible levels of contamination. When line-of-sight velocity is not available, we recover ~ 60% of such halo stars, with less than 10% contamination. When applied to the TGAS catalogue, our classifier detects 337 high confidence red giant branch halo stars. At first glance this number may seem small, however, it is consistent with the expectation from the models, given the uncertainties in the data. The large parallax errors are in fact the biggest limitation in our ability to identify a large number of halo stars in all the cases studied.

scholarly journals Star Formation Histories of Dwarf Galaxies from the Colour-Magnitude Diagrams of Their Resolved Stellar Populations

2010 ◽  
Vol 2010 ◽  
pp. 1-25 ◽  
Author(s):  
Michele Cignoni ◽  
Monica Tosi
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Dwarf Galaxies ◽  
Early Type ◽  
Significant Difference ◽  
Magnitude Diagram ◽  
The Galaxy ◽  
Show Evidence ◽  
History Of ◽  
Star Formation Histories

In this tutorial paper we summarize how the star formation (SF) history of a galactic region can be derived from the colour-magnitude diagram (CMD) of its resolved stars. The procedures to build synthetic CMDs and to exploit them to derive the SF histories (SFHs) are described, as well as the corresponding uncertainties. The SFHs of resolved dwarf galaxies of all morphological types, obtained from the application of the synthetic CMD method, are reviewed and discussed. To summarize: (1) only early-type galaxies show evidence of long interruptions in the SF activity; late-type dwarfs present rather continuous, orgasping, SF regimes; (2) a few early-type dwarfs have experienced only one episode of SF activity concentrated at the earliest epochs, whilst many others show extended or recurrent SF activity; (3) no galaxy experiencing now its first SF episode has been found yet; (4) no frequent evidence of strong SF bursts is found; (5) there is no significant difference in the SFH of dwarf irregulars and blue compact dwarfs, except for the current SF rates. Implications of these results on the galaxy formation scenarios are briefly discussed.

scholarly journals Kinematics of highly r-process-enhanced halo stars: Evidence for origins in now-destroyed ultra-faint dwarf galaxies

2019 ◽  
Vol 14 (S353) ◽  
pp. 71-74
Author(s):  
Kaley Brauer ◽  
Alexander P. Ji ◽  
Kohei Hattori ◽  
Sergio Escobar ◽  
Anna Frebel
Keyword(s):  
Milky Way ◽  
Dwarf Galaxies ◽  
Building Blocks ◽  
Specific Chemical ◽  
Halo Stars ◽  
Novel Approach ◽  
Chemical Signatures ◽  
Formation History ◽  
Stellar Halo ◽  
R Process

AbstractThe Milky Way’s stellar halo preserves a fossil record of smaller dwarf galaxies that merged with the Milky Way throughout its formation history. Currently, though, we lack reliable ways to identify which halo stars originated in which dwarf galaxies or even which stars were definitively accreted. Selecting stars with specific chemical signatures may provide a way forward. We investigate this theoretically and observationally for stars with r-process nucleosynthesis signatures. Theoretically, we combine high-resolution cosmological simulations with an empirically-motivated treatment of r-process enhancement. We find that around half of highly r-process-enhanced metal-poor halo stars may have originated in early ultra-faint dwarf galaxies that merged into the Milky Way during its formation. Observationally, we use Gaia DR2 to compare the kinematics of highly r-process-enhanced halo stars with those of normal halo stars. R-process-enhanced stars have higher galactocentric velocities than normal halo stars, suggesting an accretion origin. If r-process-enhanced stars largely originated in accreted ultra-faint dwarf galaxies, halo stars we observe today could play a key role in understanding the smallest building blocks of the Milky Way via this novel approach of chemical tagging

scholarly journals Chemical abundances of field halo stars - Implications for the building blocks of the Milky Way

2019 ◽  
Vol 14 (S351) ◽  
pp. 24-33
Author(s):  
Miho N. Ishigaki
Keyword(s):  
Milky Way ◽  
Building Blocks ◽  
Chemical Information ◽  
Wide Field ◽  
Chemical Abundance ◽  
Chemical Abundances ◽  
Halo Stars ◽  
Dimensional Phase Space ◽  
Stellar Halo ◽  
Detailed Chemical

AbstractI would like to review recent efforts of detailed chemical abundance measurements for field Milky Way halo stars. Thanks to the advent of wide-field spectroscopic surveys up to a several kpc from the Sun, large samples of field halo stars with detailed chemical measurements are continuously expanding. Combination of the chemical information and full six dimensional phase-space information is now recognized as a powerful tool to identify cosmological accretion events that have built a sizable fraction of the present-day stellar halo. Future observational prospects with wide-field spectroscopic surveys and theoretical prospects with supernova nucleosynthetic yields are also discussed.

scholarly journals Beryllium abundances and the formation of the halo and the thick disk

2009 ◽  
Vol 5 (S268) ◽  
pp. 483-488
Author(s):  
Rodolfo Smiljanic ◽  
L. Pasquini ◽  
P. Bonifacio ◽  
D. Galli ◽  
B. Barbuy ◽  
...  
Keyword(s):  
Star Formation ◽  
Formation Rate ◽  
Cosmic Ray ◽  
Thick Disk ◽  
Star Formation History ◽  
Halo Stars ◽  
Formation History ◽  
The Galaxy ◽  
History Of ◽  
Early Galaxy

AbstractThe single stable isotope of beryllium is a pure product of cosmic-ray spallation in the ISM. Assuming that the cosmic-rays are globally transported across the Galaxy, the beryllium production should be a widespread process and its abundance should be roughly homogeneous in the early-Galaxy at a given time. Thus, it could be useful as a tracer of time. In an investigation of the use of Be as a cosmochronometer and of its evolution in the Galaxy, we found evidence that in a log(Be/H) vs. [α/Fe] diagram the halo stars separate into two components. One is consistent with predictions of evolutionary models while the other is chemically indistinguishable from the thick-disk stars. This is interpreted as a difference in the star formation history of the two components and suggests that the local halo is not a single uniform population where a clear age-metallicity relation can be defined. We also found evidence that the star formation rate was lower in the outer regions of the thick disk, pointing towards an inside-out formation.

scholarly journals Extremely metal-poor stars in dwarf galaxies

2009 ◽  
Vol 5 (S265) ◽  
pp. 237-240
Author(s):  
Anna Frebel ◽  
Joshua D. Simon ◽  
Evan Kirby ◽  
Marla Geha ◽  
Beth Willman
Keyword(s):  
Galaxy Formation ◽  
Milky Way ◽  
Dwarf Galaxies ◽  
Formation Model ◽  
Abundance Pattern ◽  
Halo Stars ◽  
Abundance Patterns ◽  
Upper Limits ◽  
Stellar Halo ◽  
Metallicity Distribution

AbstractWe present Keck/HIRES spectra of six metal-poor stars in two of the ultra-faint dwarf galaxies orbiting the Milky Way, Ursa Major II and Coma Berenices, and a Magellan/MIKE spectrum of a star in the classical dwarf spheroidal galaxy (dSph) Sculptor. Our data include the first high-resolution spectroscopic observations of extremely metal-poor stars ([Fe/H] < −3.0) not belonging to the Milky Way (MW) stellar halo field population. We obtain abundance measurements and upper limits for up to 26 elements between carbon and europium. The stars span a range of −3.8 < [Fe/H] < −2.3, with the ultra-faints having large spreads in Fe. A comparison with MW halo stars of similar metallicity reveals substantial agreement between the abundance patterns of the ultra-faint dwarf galaxies and Sculptor and the MW halo for the light, α and iron-peak elements (C to Zn). This agreement contrasts with the results of earlier studies of more metal-rich stars (−2.5 ≲[Fe/H]≲ −1.0) in more luminous dwarfs, which found significant abundance discrepancies with respect to the MW halo data. The abundances of neutron-capture elements (Sr to Eu) in all three galaxies are extremely low, consistent with the most metal-poor halo stars, but not with the typical halo abundance pattern at [Fe/H]≳ −3.0. Our results are broadly consistent with a galaxy formation model which predicts that massive dwarf galaxies are the source of the metal-rich component ([Fe/H]≳ −2.5) of the MW inner halo, but we propose that dwarf galaxies similar to the dSphs are the primary contributors to the metal-poor end of the metallicity distribution of the MW outer halo.

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